This invention relates to a screen suitable for use as a precision filtering screen in various fields of industry.
Known in the art are wedge wire screens which are utilized in a broad range of industrial fields as a rugged screen which have little likelihood of clogging owing to their wires with a flat surface and a V-shaped continuous slit. These wedge wire screens are recognized as filters which are technically superior to conventional filters made of mesh-wires and punched plates.
There is however a case where a wedge wire screen of a single layer cannot perform a sufficient filtering function in some fields of industry where a precision filtering is required. In this case, it has been conventionally practiced to superpose two wedge wire screens one upon the other to cope with such precision filtering requirement.
As shown in FIG. 4A, the conventional wedge wire screen 1 is composed of a plurality of wedge wires 2 and a plurality of support rods 3, which support rods 3 are arranged with a proper interval in such a manner that they cross the wedge wires 2 and projecting portions 2b of the wedge wires 2 on the opposite side of a screen surface 2a are electrically welded to projecting portions 3a of the support rods 3. In the above described case where a single layer of such wedge wire screen 1 is not sufficient for performing a required precision filtering function, two layers of the wedge wire screens 1 are superposed one upon the other as shown in FIG. 4B to cope with such situation.
In the prior art method according to which two layers of the wedge wire screens 1 are superposed one upon the other, however, the thickness of the entire filter becomes double that of the wedge wire screen 1 of a single layer and this causes inconvenience in a case where the filtering device is limited in its structure due to spatial limitation.
Even in a case where there is no such spatial limitation, it requires a laborious work to superpose one filter upon another while taking care to secure required slits in the respective filters. Besides, such superposed filters require a frame to support the filters and an extra work to weld the filters of two layers to such frame.
Thus, the manufacturing cost of such wedge wire screens composed in two layers will become more than double that of a wedge wire screen of a single layer.
It is, therefore, an object of the present invention to overcomne the problem arising in adopting the prior art multi-layer screen in the field precision filtering and provide a multi-layer composite screen which enables to reduce total thickness of the screen and facilitates manufacturing and reduces the manufacturing cost.